replace unicode arrows

* ⇒, →, ←
* because we don't want to show them in documentation snippets and
  then it's complicated to avoid that when snippets are
  located in src/test/scala in individual modules
* dont replace object `→` in FSM.scala and PersistentFSM.scala

akka-distributed-data/src/test/scala/akka/cluster/ddata/GCounterSpec.scala

@@ -173,7 +173,7 @@ class GCounterSpec extends WordSpec with Matchers {
       val GCounter(value1) = c1
       val value2: BigInt = value1
       Changed(GCounterKey("key"))(c1) match {
-        case c @ Changed(GCounterKey("key")) ⇒
+        case c @ Changed(GCounterKey("key")) =>
           val GCounter(value3) = c.dataValue
           val value4: BigInt = value3
           value4 should be(2L)